1. Field of the Invention
This invention relates generally to the field of implantable automatic defibrillators, and relates more particularly to electrodes that may be used with such defibrillators.
It is well known in the field of cardiology that certain types of cardiac arrhythmias known as ventricular tachycardia and fibrillation can be effectively treated by the application of electrical shocks to the heart to defibrillate the fibrillating tissues. Such defibrillation may be achieved by the application by medical personnel of electrical paddles to the chest of the patient or directly to the heart tissue, if the chest is open during surgery.
More recent improvements have led to the development of implantable defibrillators which automatically monitor the heart for arrhythmia and initiate defibrillation when arrhythmia occurs. Such devices typically incorporate electrodes which are located either next to the heart or on an intravascular catheter, or both. Because the electrodes are closer to the heart tissue, implanted defibrillators require less electrical energy to stimulate the heart than external electrodes.
However, major surgery is generally necessary to implant present defibrillator lead systems, such as a median sternotomy or lateral thoractomy. These procedures can be very traumatic to the patient, and may have adverse side effects such as surgical complications, morbidity or mortality. Because of these risks, only those persons whose condition is so dire that the potential benefits outweight the risks are suitable candidates for such surgery, thus excluding many patients who might otherwise benefit from the surgery.
2. Description of the Relevant Art
There have been various attempts to solve these problems, such as that of Heilman, U.S. Pat. No. 4,291,707, and Heilman, U.S. Pat. No. 4,270,549, which respectively show an electrode and the method of implanting it. Heilman teaches the use of rectangular paddle electrodes measuring 4 cm. by 6 cm. Two such electrodes are used, requiring two incisions, one in the abdominal wall and one in the interior thoracic region. Alternatively, one paddle electrode may be inserted through an incision and another intravasculr electrode inserted into the superior vena cava. This still requires two separate intrusions into the body, however.
Another attempted solution involves the use of bipolar electrodes, i.e. a single assembly that contains both electrodes, so that only that single assembly need be put in contact with the heart tissue. Such electrodes are shown in Ackerman, U.S. Pat. No. Re. 27,569, and Alferness, U.S. Pat. No. 4,355,642. However, it is believed that better results are obtained by locating the electrodes on opposite sides of the heart, either side to side or front to back.
Other types of electrodes, some of which may be used transvenously, are shown in Williamson, U.S. Pat. No. 3,749,101, Kallok et al., U.S. Pat. No. 4,355,646, and Moore, U.S. Pat. No. 4,567,900.
It is believed that none of these devices meet the need for an implantable electrode that may be inserted with minimal trauma to the patient while providing adequate surface area for defibrillation.